1. Field of Invention
The present invention relates to a high pressure fuel pump applied to a common rail system of a diesel engine; and, particularly, to a high pressure fuel pump of which an inner portion is formed with a lubrication passage in which fuel flows to allow components in the high pressure fuel pump to be lubricated, thereby having improved lubrication characteristics.
2. Description of Related Art
A common rail system mounted to a diesel engine is provided with a high pressure fuel pump into which fuel primarily pressurized by a low pressure fuel pump is introduced from a fuel tank and from which the introduced fuel is discharged by being secondarily pressurized at a high pressure of 2000 bar or more.
A schematic structure of such a high pressure fuel pump is described with reference to FIG. 1. The high pressure fuel pump includes a housing 110 having an inlet 111 and an outlet 112, a cam shaft 120 which is rotatably provided within the housing 110 and formed with a cam 121, a plunger 130 which is lifted by rotation of the cam shaft 120 to pressurize the fuel, a tappet body 131 to support a lower end of the plunger 130, and a roller 142 provided between the tappet body 131 and the cam 121.
When the cam shaft 120 rotates, the plunger 130 pressurizes the fuel, which is introduced into a high pressure chamber formed within the housing 110 through the inlet 111, at a high pressure to discharge the fuel to the outlet 112 while being lifted and dropped along at least one cam 121 formed around the cam shaft 120.
In this case, the roller 142 is mounted to a roller shoe 141 pressed in the tappet body 131 and is maintained in a state of contact with the cam 121 during the rotation of the cam shaft 120, to thereby reduce friction between the cam 121 and the roller shoe 141.
However, the roller 142 is always in contact with the cam 121 by the tappet body 131 supported by a spring 132, and moreover is inserted in a state of keeping a certain clearance with the roller shoe 141.
According to the structure of the high pressure fuel pump 100 of the related art, the fuel serving as a lubricant is not sufficiently supplied to a clearance between the roller 142 and the roller shoe 141 indicated by “A” in FIGS. 2 and 3 in which the roller 142 comes into contact with the roller shoe 141 and a contact portion between the roller 142 and the cam 121 indicated by “B” in FIGS. 2 and 3, thereby not causing smooth lubrication action. That is, the roller 142 is in surface contact with the roller shoe 141 on a portion indicated by “A”, and the roller 142 is in line contact with the cam 121 on a portion indicated by “B”. Accordingly, there is a problem in that the roller 142, the roller shoe 141, or the cam 121 is worn out or burned on the contact surface between the roller 142 and the roller shoe 141 and on the contact portion between the roller 142 and the cam 121 depending on these operations.
Therefore, the fuel serving as a lubricant needs to be sufficiently supplied in order to reduce friction on the contact surface and the contact portion. If the lubrication is abnormal, the cam 121 of the cam shaft 120, the roller 142, and the roller shoe 141 are worn out. Moreover, in the worst case, a fatal failure such as burning of the high pressure fuel pump 100 is caused.
In particular, the roller 142 mounted within the roller shoe 141 is kept at a minimal clearance. Hence, in a case where the lubrication is not smooth, abrasion between the roller 142 and the roller shoe 141 may be immediately caused.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.